Degrees of freedom of three-user SISO interference channels under hybrid CSI at the transmitters

In this paper, we consider the degrees of freedom (DoF) of the three-user single-input-single-output interference channel (SISO-IC) with independent and identically distributed (i.i.d.) fading across antennas and channel uses and under hybrid channel state information (CSI) at the transmitters. Hybrid CSI implies that delayed CSI of the whole network is available to all the transmitters whereas only local instantaneous CSI is available to each transmitter which is obtained through feedback from its own receiver. We show that a DoF of 6 can be attained for this scenario which is greater than the existing results on completely delayed CSI feedback scenario. Further, the local instantaneous CSIT needs to be available only for 20% of the total transmission time. In other words, the CSIT in our scheme can be delayed up to 80% of the channel coherence time. Also, the message for every user is completely private, i.e., any part of it cannot be decoded by any unintended user.